Yet, I dont believe the role of the Cleric is overly inflated in D&D Next. If I were to place the D&D Next cleric within the context of Clerics from all editions, I'd say his relative impact on the game is greater than AD&D, but not nearly as inflated as 3e and 4e Clerics.
I wonder sometimes if the 3e cleric was a victim of its own hype, so to speak. Because the discussion on game balance decisions made about the system was made very public, a lot of the assumptions that were used as the baseline for game balance (i.e., the four-member traditional adventuring group, with a scouting/trapfinding optimized rogue, a heavy-armor wearing fighter/tank, a magic-missile and fireball slinging wizard, and a healing and buff-dealing cleric) I think a lot of people fell victim to confirmation bias.
Either that or so many encounters were designed specifically with those assumptions in mind that it led to confirmation bias of another kind--because encounters were designed with the four-roles in mind, lack of the four roles led to more failure.
In AD&D (or BD&D or OD&D, or whatever), all of those assumptions were much more subtle, and therefore parties that didn't necessarily have them could muddle through. A good GM who managed to "tweak" the experience slightly to account for what the party was missing, could make sure that the party had a good time and were successful. Unless, of course, they played in the "skilled play" mindset, in which case, the four role party was already fairly well established. But outside of the skilled play mindset, I don't think many gamers necessarily gave this notion nearly as much thought.
With the assumptions more "nakedly visible", so to speak, a lot of that intuitive tweaking was simply not done, I think. It was just assumed that you needed to match the design assumptions to be successful. And if you struggled but didn't meet the assumptions, well, hey... of course not! You don't have a cleric! (or whatever.)